Field of the Invention
The present invention relates to an electrode material and a method for manufacturing the same.
Description of Related Art
In recent years, as a battery anticipated to have a small size, a light weight, and high capacity, a non-aqueous electrolytic solution-based secondary battery such as a lithium ion battery has been proposed and put into practical use. The lithium ion battery is configured to have a positive electrode and a negative electrode which have properties capable of reversibly intercalating and deintercalating lithium ions, and a non-aqueous electrolyte.
Regarding a negative electrode material for the lithium ion battery, as a negative electrode active material, generally, a carbon-based material or a lithium-containing metal oxide having properties capable of reversibly intercalating and deintercalating lithium ions such as lithium titanate (Li4Ti5O12) is used.
On the other hand, regarding a positive electrode material for the lithium ion battery, as a positive electrode active material, a lithium-containing metal oxide having properties capable of reversibly intercalating and deintercalating lithium ions such as lithium iron phosphate (LiFePO4) or an electrode material mixture including a binder and the like is used. In addition, when the electrode material mixture is applied to the surface of a metal foil called a collector, the positive electrode in the lithium ion battery is formed.
Compared with secondary batteries of the related art such as lead batteries, nickel-cadmium batteries, and nickel-hydrogen batteries, the lithium ion batteries have a lighter weight, a smaller size, and higher energy. Therefore, the lithium ion batteries are used not only as small-size power supplies in portable electronic devices such as mobile phones and notebook personal computers but also as large-size stationary emergency power supplies.
In addition, recently, studies have been underway regarding the use of lithium ion batteries as high-output power supplies for plug-in hybrid vehicles, hybrid vehicles, and electric power tools. Batteries used as the high-output power supplies are required to have high-speed charge and discharge characteristics.
Among the electrode active materials, the lithium oxoacid salt-based compound (particularly, lithium iron phosphate) is attracting attention due to the excellent safety and the absence of problems with its resource and cost. However, the lithium oxoacid salt-based compound has a problem with low electron conductivity due to its crystal structure (olivine-type crystal structure).
Therefore, in order to increase the electron conductivity of an electrode material for which the lithium oxoacid salt-based compound is used as an electrode active material, means of JP-A-2001-15111 has been proposed. In JP-A-2001-15111, particle surfaces of an electrode active material made of lithium iron phosphate are covered with an organic compound that is a carbon source, then, the organic compound is carbonized so as to form a carbonaceous film on the surface of the electrode active material, and carbon in the carbonaceous film is made to act as an electron conductive substance.
In addition, JP-A-2014-216241 discloses that, in order to improve not only the electron conductivity but also the lithium ion conductivity, the electrode material is provided with a configuration in which a carbonaceous film containing an ion conductive substance is formed on the surfaces of electrode active material particles.
Furthermore, JP-T-2008-507832 discloses that, in order to restrict the growth of the fine crystals of a positive electrode active material, at least one precursor of the positive electrode active material and a specific additional compound (including an oxide such as Al2O3, TiO2, ZrO2, or Fe2O3) are thermally treated.
In JP-T-2010-529593, in order to increase the capacity of the lithium ion secondary battery, a positive electrode active material for a lithium ion battery is configured to include a sintered product formed by sintering lithium iron phosphate together with at least one metal oxide.